1. Field of the Invention
The present invention relates to an ink jet recording apparatus that uses a recording head that discharges droplets of ink by creating a bubble in the ink by using thermal energy produced by a heater, i.e., an electrothermal transducer. The ink jet recording apparatus records various kinds of information, including an image, on a recording medium by placing droplets of recording ink discharged from nozzles of the recording head onto the recording medium.
2. Description of the Related Art
One known example of such an ink jet recording method, which places ink onto a recording medium, such as a sheet of paper, by discharging the ink (droplets of recording ink) from discharge ports of a recording head, is a discharge method in which thermal energy is applied to ink to discharge the ink from the discharge ports. This discharge method is advantageous in that a high-density multi-nozzle recording head can be easily realized. However, an ink jet recording apparatus that uses a recording head operating in such a discharge method may suffer from a discharge defect occurring in the entire recording head or part of nozzles because of clogging of a nozzle caused by a foreign object, of a bubble undesirably introduced in an ink supply channel, or of a change in wettability of a nozzle surface.
When a discharge defect occurs in a nozzle of a recording head, a recovery operation for recovering a discharge state can be executed. In the case of a so-called serial ink jet recording apparatus, which records information by alternately repeating a scan by a recording head in the forward and reverse directions and a conveyance of a recording sheet being a recording medium, the recovery operation can be executed after the recording head is moved outside the recording sheet. In contrast to this, in the case of a full-line type recording apparatus, in which nozzles corresponding to the entire width of a recording medium are arranged in rows, a recording operation is significantly fast, and the recording head cannot be moved outside the recording medium during the recording operation. Therefore, it is desirable to immediately locate a nozzle suffering from a discharge defect and, when the defective nozzle is located, to utilize the detective nozzle location information for compensating for the defect to form a correct image and for a recovery operation for a recording head.
To address this problem of discharge defects, there has been proposed various methods for detecting the presence of a discharge defect, for compensating for the discharge defect, control methods, apparatuses, various methods for controlling the amount of discharge, and apparatuses therefor.
Japanese Patent Laid-Open No. 6-079956 discloses an example of a printing method that determines a printed article to obtain a defect-free image. This method prints a predetermined pattern on a sheet for detection, reads the printed pattern by a reading device, and detects an abnormal print element. More specifically, the structure moves image data to be applied to the abnormal print element so that the image data is superimposed on image data for another print element to compensate for defects that would occur in printing to obtain a defect-free image.
For a structure that uses a recording head having a width equal to the sheet width, the use of a detecting unit (reading head) configured to detect whether ink has been discharged to equalize the discharge state in the ink jet recording head is known. For example, Japanese Patent Laid-Open No. 3-234636 discloses a structure that includes a detecting unit configured to detect whether ink has been discharged and sets control in accordance with the detected drive condition.
In addition, U.S. Pat. No. 5,530,462 discloses a method for detecting flying ink droplets for use in a structure that includes a set of a light emitting element and a light receiving element disposed adjacent to both ends of an array of discharge ports of a recording head. This method determine a discharge state of the recording liquid for each discharge port by using a detecting unit configured to detect discharged recording liquid. U.S. Pat. No. 4,550,327 discloses a structure that determines a discharge state at a discharging source. The structure includes a conductive element disposed at a position subjected to thermal effects produced by a heater and detects a change in resistance varying depending on the temperature.
U.S. Pat. No. 6,074,034 discloses another structure for detecting ink droplets at a discharging source. The structure includes heaters and a temperature detecting element disposed on the same support (e.g., a silicon substrate). In this structure, the film temperature detecting element is disposed so as to overlap a region where the heaters are arranged. The structure determines a discharge defect on the basis a change in resistance of the temperature detecting element varying with the change in temperature. In addition, the film temperature detecting element is formed on a heater board by a deposition process, and a terminal thereof is connected to the exterior by wire bonding.
The method for detecting an abnormal state of a nozzle disclosed in Japanese Patent Laid-Open No. 6-079956, described above, detects an abnormal print element from a result of reading a check pattern printed on a sheet of paper. It is thus necessary to print the pattern before detection of a discharge defect, and therefore, it is significantly difficult to immediately detect a discharge defect. Moreover, a reading device is required, so the equipment cost is undesirably increased.
For the structures disclosed in Japanese Patent Laid-Open No. 3-234636 and U.S. Pat. No. 5,530,462, described above, it is difficult to miniaturize the apparatus and reduce the cost and also hard to immediately detect a nozzle suffering from a discharge defect.
The patent documents described above do not disclose a structure that can immediately detect a discharge defect for each nozzle without having to increase equipment size.